Microstructure and optical properties of nanostructured silicon thin films and artificial dielectrics

Thin films on various substrates and artificial dielectrics in fused silica composed of silicon nanoclusters and nanocrystals, have been grown by excimer laser ablation and Si ion implantation, respectively. The nanoscale structure of the laser ablated films have been shown by conventional and surface-enhanced micro-Raman scattering and transmission electron microscopy to be composed of silicon droplets surrounded by silicon nanoclusters. The droplets are composed of micro- and nano-crystalline silicon embedded in silicon nanoclusters. The as-prepared ion implanted samples are composed of silicon nanoclusters only, but on annealing, silicon nanocrystals and larger nanoclusters are precipitated. The as-prepared and annealed ion implanted samples, show size-dependent visible photoluminescence, while the laser ablated films show weak visible photoluminescence on annealing and large optical non-linear responses - the latter probably due to inter-cluster coupling within the droplets.